stmhal: Overhaul UART class to use read/write, and improve it.v1.3.4

UART object now uses a stream-like interface: read, readall, readline,
readinto, readchar, write, writechar.

Timeouts are configured when the UART object is initialised, using
timeout and timeout_char keyword args.

The object includes optional read buffering, using interrupts.  You can set
the buffer size dynamically using read_buf_len keyword arg.  A size of 0
disables buffering.

8 files changed, 449 insertions, 199 deletions

diff --git a/stmhal/main.c b/stmhal/main.c
index 74a9c4c05..097b8ca85 100644
--- a/stmhal/main.c
+++ b/stmhal/main.c
@@ -320,6 +320,7 @@ soft_reset:
     pin_init0();
     extint_init0();
     timer_init0();
+    uart_init0();
 
 #if MICROPY_HW_ENABLE_RNG
     rng_init0();
@@ -543,6 +544,7 @@ soft_reset:
 
     printf("PYB: soft reboot\n");
     timer_deinit();
+    uart_deinit();
 
     first_soft_reset = false;
     goto soft_reset;
diff --git a/stmhal/qstrdefsport.h b/stmhal/qstrdefsport.h
index 075cfe2f7..314fceea5 100644
--- a/stmhal/qstrdefsport.h
+++ b/stmhal/qstrdefsport.h
@@ -143,11 +143,17 @@ Q(baudrate)
 Q(bits)
 Q(stop)
 Q(parity)
+Q(read_buf_len)
+Q(buf)
+Q(len)
+Q(timeout)
+Q(timeout_char)
 Q(init)
 Q(deinit)
-Q(all)
-Q(send)
-Q(recv)
+Q(any)
+Q(writechar)
+Q(readchar)
+Q(readinto)
 
 // for CAN class
 Q(CAN)
diff --git a/stmhal/stm32f4xx_it.c b/stmhal/stm32f4xx_it.c
index 74fdf53d1..eb65b1a54 100644
--- a/stmhal/stm32f4xx_it.c
+++ b/stmhal/stm32f4xx_it.c
@@ -76,6 +76,7 @@
 #include "obj.h"
 #include "extint.h"
 #include "timer.h"
+#include "uart.h"
 #include "storage.h"
 
 extern void __fatal_error(const char*);
@@ -395,3 +396,24 @@ void TIM8_UP_TIM13_IRQHandler(void) {
 void TIM8_TRG_COM_TIM14_IRQHandler(void) {
     timer_irq_handler(14);
 }
+
+// UART/USART IRQ handlers
+void USART1_IRQHandler(void) {
+    uart_irq_handler(1);
+}
+
+void USART2_IRQHandler(void) {
+    uart_irq_handler(2);
+}
+
+void USART3_IRQHandler(void) {
+    uart_irq_handler(3);
+}
+
+void UART4_IRQHandler(void) {
+    uart_irq_handler(4);
+}
+
+void USART6_IRQHandler(void) {
+    uart_irq_handler(6);
+}
diff --git a/stmhal/uart.c b/stmhal/uart.c
index 68c9be864..9abe4713e 100644
--- a/stmhal/uart.c
+++ b/stmhal/uart.c
@@ -37,7 +37,7 @@
 #include "qstr.h"
 #include "obj.h"
 #include "runtime.h"
-#include "bufhelper.h"
+#include "stream.h"
 #include "uart.h"
 #include "pybioctl.h"
 
@@ -45,41 +45,97 @@
 /// \class UART - duplex serial communication bus
 ///
 /// UART implements the standard UART/USART duplex serial communications protocol.  At
-/// the physical level it consists of 2 lines: RX and TX.
+/// the physical level it consists of 2 lines: RX and TX.  The unit of communication
+/// is a character (not to be confused with a string character) which can be 8 or 9
+/// bits wide.
 ///
-/// See usage model of I2C.  UART is very similar.  Main difference is
-/// parameters to init the UART bus:
+/// UART objects can be created and initialised using:
 ///
 ///     from pyb import UART
 ///
 ///     uart = UART(1, 9600)                         # init with given baudrate
-///     uart.init(9600, bits=8, stop=1, parity=None) # init with given parameters
+///     uart.init(9600, bits=8, parity=None, stop=1) # init with given parameters
 ///
-/// Bits can be 8 or 9, stop can be 1 or 2, parity can be None, 0 (even), 1 (odd).
+/// Bits can be 8 or 9.  Parity can be None, 0 (even) or 1 (odd).  Stop can be 1 or 2.
 ///
-/// Extra method:
+/// A UART object acts like a stream object and reading and writing is done
+/// using the standard stream methods:
+///
+///     uart.read(10)       # read 10 characters, returns a bytes object
+///     uart.readall()      # read all available characters
+///     uart.readline()     # read a line
+///     uart.readinto(buf)  # read and store into the given buffer
+///     uart.write('abc')   # write the 3 characters
+///
+/// Individual characters can be read/written using:
+///
+///     uart.readchar()     # read 1 character and returns it as an integer
+///     uart.writechar(42)  # write 1 character
+///
+/// To check if there is anything to be read, use:
 ///
 ///     uart.any()               # returns True if any characters waiting
 
+#define CHAR_WIDTH_8BIT (0)
+#define CHAR_WIDTH_9BIT (1)
+
 struct _pyb_uart_obj_t {
     mp_obj_base_t base;
     pyb_uart_t uart_id;
     bool is_enabled;
     UART_HandleTypeDef uart;
+    IRQn_Type irqn;
+    uint16_t timeout;                   // timeout waiting for first char
+    uint16_t timeout_char;              // timeout waiting between chars
+    uint16_t char_width;                // 0 for 7,8 bit chars, 1 for 9 bit chars
+    uint16_t read_buf_len;              // len in chars; buf can hold len-1 chars
+    volatile uint16_t read_buf_head;    // indexes first empty slot
+    uint16_t read_buf_tail;             // indexes first full slot (not full if equals head)
+    byte *read_buf;                     // byte or uint16_t, depending on char size
 };
 
+// this table converts from HAL_StatusTypeDef to POSIX errno
+STATIC const byte hal_status_to_errno_table[4] = {
+    [HAL_OK] = 0,
+    [HAL_ERROR] = EIO,
+    [HAL_BUSY] = EBUSY,
+    [HAL_TIMEOUT] = ETIMEDOUT,
+};
+
+// pointers to all UART objects (if they have been created)
+STATIC pyb_uart_obj_t *pyb_uart_obj_all[6];
+
+STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in);
+
+void uart_init0(void) {
+    for (int i = 0; i < MP_ARRAY_SIZE(pyb_uart_obj_all); i++) {
+        pyb_uart_obj_all[i] = NULL;
+    }
+}
+
+// unregister all interrupt sources
+void uart_deinit(void) {
+    for (int i = 0; i < MP_ARRAY_SIZE(pyb_uart_obj_all); i++) {
+        pyb_uart_obj_t *uart_obj = pyb_uart_obj_all[i];
+        if (uart_obj != NULL) {
+            pyb_uart_deinit(uart_obj);
+        }
+    }
+}
+
 // assumes Init parameters have been set up correctly
 bool uart_init2(pyb_uart_obj_t *uart_obj) {
-    USART_TypeDef *UARTx = NULL;
-
-    uint32_t GPIO_Pin = 0;
-    uint8_t  GPIO_AF_UARTx = 0;
+    USART_TypeDef *UARTx;
+    IRQn_Type irqn;
+    uint32_t GPIO_Pin;
+    uint8_t GPIO_AF_UARTx = 0;
     GPIO_TypeDef* GPIO_Port = NULL;
 
     switch (uart_obj->uart_id) {
         // USART1 is on PA9/PA10 (CK on PA8), PB6/PB7
         case PYB_UART_1:
             UARTx = USART1;
+            irqn = USART1_IRQn;
             GPIO_AF_UARTx = GPIO_AF7_USART1;
 
 #if defined (PYBV4) || defined(PYBV10)
@@ -96,6 +152,7 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
         // USART2 is on PA2/PA3 (CK on PA4), PD5/PD6 (CK on PD7)
         case PYB_UART_2:
             UARTx = USART2;
+            irqn = USART2_IRQn;
             GPIO_AF_UARTx = GPIO_AF7_USART2;
 
             GPIO_Port = GPIOA;
@@ -107,6 +164,7 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
         // USART3 is on PB10/PB11 (CK on PB12), PC10/PC11 (CK on PC12), PD8/PD9 (CK on PD10)
         case PYB_UART_3:
             UARTx = USART3;
+            irqn = USART3_IRQn;
             GPIO_AF_UARTx = GPIO_AF7_USART3;
 
 #if defined(PYBV3) || defined(PYBV4) | defined(PYBV10)
@@ -122,6 +180,7 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
         // UART4 is on PA0/PA1, PC10/PC11
         case PYB_UART_4:
             UARTx = UART4;
+            irqn = UART4_IRQn;
             GPIO_AF_UARTx = GPIO_AF8_UART4;
 
             GPIO_Port = GPIOA;
@@ -133,6 +192,7 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
         // USART6 is on PC6/PC7 (CK on PC8)
         case PYB_UART_6:
             UARTx = USART6;
+            irqn = USART6_IRQn;
             GPIO_AF_UARTx = GPIO_AF8_USART6;
 
             GPIO_Port = GPIOC;
@@ -145,6 +205,9 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
             return false;
     }
 
+    uart_obj->irqn = irqn;
+    uart_obj->uart.Instance = UARTx;
+
     // init GPIO
     GPIO_InitTypeDef GPIO_InitStructure;
     GPIO_InitStructure.Pin = GPIO_Pin;
@@ -155,7 +218,6 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
     HAL_GPIO_Init(GPIO_Port, &GPIO_InitStructure);
 
     // init UARTx
-    uart_obj->uart.Instance = UARTx;
     HAL_UART_Init(&uart_obj->uart);
 
     uart_obj->is_enabled = true;
@@ -163,6 +225,7 @@ bool uart_init2(pyb_uart_obj_t *uart_obj) {
     return true;
 }
 
+/* obsolete and unused
 bool uart_init(pyb_uart_obj_t *uart_obj, uint32_t baudrate) {
     UART_HandleTypeDef *uh = &uart_obj->uart;
     memset(uh, 0, sizeof(*uh));
@@ -175,53 +238,54 @@ bool uart_init(pyb_uart_obj_t *uart_obj, uint32_t baudrate) {
     uh->Init.OverSampling = UART_OVERSAMPLING_16;
     return uart_init2(uart_obj);
 }
+*/
 
-void uart_deinit(pyb_uart_obj_t *uart_obj) {
-    uart_obj->is_enabled = false;
-    UART_HandleTypeDef *uart = &uart_obj->uart;
-    HAL_UART_DeInit(uart);
-    if (uart->Instance == USART1) {
-        __USART1_FORCE_RESET();
-        __USART1_RELEASE_RESET();
-        __USART1_CLK_DISABLE();
-    } else if (uart->Instance == USART2) {
-        __USART2_FORCE_RESET();
-        __USART2_RELEASE_RESET();
-        __USART2_CLK_DISABLE();
-    } else if (uart->Instance == USART3) {
-        __USART3_FORCE_RESET();
-        __USART3_RELEASE_RESET();
-        __USART3_CLK_DISABLE();
-    } else if (uart->Instance == UART4) {
-        __UART4_FORCE_RESET();
-        __UART4_RELEASE_RESET();
-        __UART4_CLK_DISABLE();
-    } else if (uart->Instance == USART6) {
-        __USART6_FORCE_RESET();
-        __USART6_RELEASE_RESET();
-        __USART6_CLK_DISABLE();
-    }
+bool uart_rx_any(pyb_uart_obj_t *self) {
+    return self->read_buf_tail != self->read_buf_head
+        || __HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET;
 }
 
-bool uart_rx_any(pyb_uart_obj_t *uart_obj) {
-    return __HAL_UART_GET_FLAG(&uart_obj->uart, UART_FLAG_RXNE);
+// Waits at most timeout milliseconds for at least 1 char to become ready for
+// reading (from buf or for direct reading).
+// Returns true if something available, false if not.
+STATIC bool uart_rx_wait(pyb_uart_obj_t *self, uint32_t timeout) {
+    uint32_t start = HAL_GetTick();
+    for (;;) {
+        if (self->read_buf_tail != self->read_buf_head || __HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET) {
+            return true; // have at least 1 char ready for reading
+        }
+        if (HAL_GetTick() - start >= timeout) {
+            return false; // timeout
+        }
+        __WFI();
+    }
 }
 
-int uart_rx_char(pyb_uart_obj_t *uart_obj) {
-    uint8_t ch;
-    if (HAL_UART_Receive(&uart_obj->uart, &ch, 1, 0) != HAL_OK) {
-        ch = 0;
+// assumes there is a character available
+int uart_rx_char(pyb_uart_obj_t *self) {
+    if (self->read_buf_tail != self->read_buf_head) {
+        // buffering via IRQ
+        int data;
+        if (self->char_width == CHAR_WIDTH_9BIT) {
+            data = ((uint16_t*)self->read_buf)[self->read_buf_tail];
+        } else {
+            data = self->read_buf[self->read_buf_tail];
+        }
+        self->read_buf_tail = (self->read_buf_tail + 1) % self->read_buf_len;
+        return data;
+    } else {
+        // no buffering
+        return self->uart.Instance->DR;
     }
-    return ch;
 }
 
-void uart_tx_char(pyb_uart_obj_t *uart_obj, int c) {
+STATIC void uart_tx_char(pyb_uart_obj_t *uart_obj, int c) {
     uint8_t ch = c;
-    HAL_UART_Transmit(&uart_obj->uart, &ch, 1, 100000);
+    HAL_UART_Transmit(&uart_obj->uart, &ch, 1, uart_obj->timeout);
 }
 
 void uart_tx_strn(pyb_uart_obj_t *uart_obj, const char *str, uint len) {
-    HAL_UART_Transmit(&uart_obj->uart, (uint8_t*)str, len, 100000);
+    HAL_UART_Transmit(&uart_obj->uart, (uint8_t*)str, len, uart_obj->timeout);
 }
 
 void uart_tx_strn_cooked(pyb_uart_obj_t *uart_obj, const char *str, uint len) {
@@ -233,6 +297,36 @@ void uart_tx_strn_cooked(pyb_uart_obj_t *uart_obj, const char *str, uint len) {
     }
 }
 
+// this IRQ handler is set up to handle RXNE interrupts only
+void uart_irq_handler(mp_uint_t uart_id) {
+    // get the uart object
+    pyb_uart_obj_t *self = pyb_uart_obj_all[uart_id - 1];
+
+    if (self == NULL) {
+        // UART object has not been set, so we can't do anything, not
+        // even disable the IRQ.  This should never happen.
+        return;
+    }
+
+    if (__HAL_UART_GET_FLAG(&self->uart, UART_FLAG_RXNE) != RESET) {
+        int data = self->uart.Instance->DR; // clears UART_FLAG_RXNE
+        if (self->read_buf_len != 0) {
+            uint16_t next_head = (self->read_buf_head + 1) % self->read_buf_len;
+            if (next_head != self->read_buf_tail) {
+                // only store data if room in buf
+                if (self->char_width == CHAR_WIDTH_9BIT) {
+                    ((uint16_t*)self->read_buf)[self->read_buf_head] = data;
+                } else {
+                    self->read_buf[self->read_buf_head] = data;
+                }
+                self->read_buf_head = next_head;
+            }
+        } else {
+            // TODO set flag for buffer overflow
+        }
+    }
+}
+
 /******************************************************************************/
 /* Micro Python bindings                                                      */
 
@@ -241,61 +335,96 @@ STATIC void pyb_uart_print(void (*print)(void *env, const char *fmt, ...), void
     if (!self->is_enabled) {
         print(env, "UART(%u)", self->uart_id);
     } else {
-        print(env, "UART(%u, baudrate=%u, bits=%u, stop=%u",
+        print(env, "UART(%u, baudrate=%u, bits=%u, parity=",
             self->uart_id, self->uart.Init.BaudRate,
-            self->uart.Init.WordLength == UART_WORDLENGTH_8B ? 8 : 9,
-            self->uart.Init.StopBits == UART_STOPBITS_1 ? 1 : 2);
+            self->uart.Init.WordLength == UART_WORDLENGTH_8B ? 8 : 9);
         if (self->uart.Init.Parity == UART_PARITY_NONE) {
-            print(env, ", parity=None)");
+            print(env, "None");
         } else {
-            print(env, ", parity=%u)", self->uart.Init.Parity == UART_PARITY_EVEN ? 0 : 1);
+            print(env, "%u", self->uart.Init.Parity == UART_PARITY_EVEN ? 0 : 1);
         }
+        print(env, ", stop=%u, timeout=%u, timeout_char=%u, read_buf_len=%u)",
+            self->uart.Init.StopBits == UART_STOPBITS_1 ? 1 : 2,
+            self->timeout, self->timeout_char, self->read_buf_len);
     }
 }
 
-/// \method init(baudrate, *, bits=8, stop=1, parity=None)
+/// \method init(baudrate, bits=8, parity=None, stop=1, *, timeout=1000, timeout_char=0, read_buf_len=64)
 ///
 /// Initialise the UART bus with the given parameters:
 ///
 ///   - `baudrate` is the clock rate.
 ///   - `bits` is the number of bits per byte, 8 or 9.
-///   - `stop` is the number of stop bits, 1 or 2.
 ///   - `parity` is the parity, `None`, 0 (even) or 1 (odd).
-STATIC const mp_arg_t pyb_uart_init_args[] = {
-    { MP_QSTR_baudrate, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 9600} },
-    { MP_QSTR_bits,     MP_ARG_KW_ONLY | MP_ARG_INT,  {.u_int = 8} },
-    { MP_QSTR_stop,     MP_ARG_KW_ONLY | MP_ARG_INT,  {.u_int = 1} },
-    { MP_QSTR_parity,   MP_ARG_KW_ONLY | MP_ARG_OBJ,  {.u_obj = mp_const_none} },
-};
-#define PYB_UART_INIT_NUM_ARGS MP_ARRAY_SIZE(pyb_uart_init_args)
+///   - `stop` is the number of stop bits, 1 or 2.
+///   - `timeout` is the timeout in milliseconds to wait for the first character.
+///   - `timeout_char` is the timeout in milliseconds to wait between characters.
+///   - `read_buf_len` is the character length of the read buffer (0 to disable).
+STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_baudrate, MP_ARG_REQUIRED | MP_ARG_INT, {.u_int = 9600} },
+        { MP_QSTR_bits, MP_ARG_INT, {.u_int = 8} },
+        { MP_QSTR_parity, MP_ARG_OBJ, {.u_obj = mp_const_none} },
+        { MP_QSTR_stop, MP_ARG_INT, {.u_int = 1} },
+        { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1000} },
+        { MP_QSTR_timeout_char, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
+        { MP_QSTR_read_buf_len, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 64} },
+    };
 
-STATIC mp_obj_t pyb_uart_init_helper(pyb_uart_obj_t *self, mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
     // parse args
-    mp_arg_val_t vals[PYB_UART_INIT_NUM_ARGS];
-    mp_arg_parse_all(n_args, args, kw_args, PYB_UART_INIT_NUM_ARGS, pyb_uart_init_args, vals);
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
 
     // set the UART configuration values
     memset(&self->uart, 0, sizeof(self->uart));
     UART_InitTypeDef *init = &self->uart.Init;
-    init->BaudRate = vals[0].u_int;
-    init->WordLength = vals[1].u_int == 8 ? UART_WORDLENGTH_8B : UART_WORDLENGTH_9B;
-    switch (vals[2].u_int) {
-        case 1: init->StopBits = UART_STOPBITS_1; break;
-        default: init->StopBits = UART_STOPBITS_2; break;
-    }
-    if (vals[3].u_obj == mp_const_none) {
+    init->BaudRate = args[0].u_int;
+    init->WordLength = args[1].u_int == 8 ? UART_WORDLENGTH_8B : UART_WORDLENGTH_9B;
+    if (args[2].u_obj == mp_const_none) {
         init->Parity = UART_PARITY_NONE;
     } else {
-        mp_int_t parity = mp_obj_get_int(vals[3].u_obj);
+        mp_int_t parity = mp_obj_get_int(args[2].u_obj);
         init->Parity = (parity & 1) ? UART_PARITY_ODD : UART_PARITY_EVEN;
     }
+    switch (args[3].u_int) {
+        case 1: init->StopBits = UART_STOPBITS_1; break;
+        default: init->StopBits = UART_STOPBITS_2; break;
+    }
     init->Mode = UART_MODE_TX_RX;
     init->HwFlowCtl = UART_HWCONTROL_NONE;
     init->OverSampling = UART_OVERSAMPLING_16;
 
     // init UART (if it fails, it's because the port doesn't exist)
     if (!uart_init2(self)) {
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART port %d does not exist", self->uart_id));
+        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%d) does not exist", self->uart_id));
+    }
+
+    // set timeouts
+    self->timeout = args[4].u_int;
+    self->timeout_char = args[5].u_int;
+
+    // setup the read buffer
+    m_del(byte, self->read_buf, self->read_buf_len << self->char_width);
+    if (init->WordLength == UART_WORDLENGTH_9B && init->Parity == UART_PARITY_NONE) {
+        self->char_width = CHAR_WIDTH_9BIT;
+    } else {
+        self->char_width = CHAR_WIDTH_8BIT;
+    }
+    self->read_buf_head = 0;
+    self->read_buf_tail = 0;
+    if (args[6].u_int <= 0) {
+        // no read buffer
+        self->read_buf_len = 0;
+        self->read_buf = NULL;
+        HAL_NVIC_DisableIRQ(self->irqn);
+        __HAL_UART_DISABLE_IT(&self->uart, UART_IT_RXNE);
+    } else {
+        // read buffer using interrupts
+        self->read_buf_len = args[6].u_int;
+        self->read_buf = m_new(byte, args[6].u_int << self->char_width);
+        __HAL_UART_ENABLE_IT(&self->uart, UART_IT_RXNE);
+        HAL_NVIC_SetPriority(self->irqn, 0xd, 0xd); // next-to-next-to lowest priority
+        HAL_NVIC_EnableIRQ(self->irqn);
     }
 
     return mp_const_none;
@@ -320,41 +449,51 @@ STATIC mp_obj_t pyb_uart_make_new(mp_obj_t type_in, mp_uint_t n_args, mp_uint_t
     // check arguments
     mp_arg_check_num(n_args, n_kw, 1, MP_OBJ_FUN_ARGS_MAX, true);
 
-    // create object
-    pyb_uart_obj_t *o = m_new_obj(pyb_uart_obj_t);
-    o->base.type = &pyb_uart_type;
-    o->is_enabled = false;
-
     // work out port
-    o->uart_id = 0;
+    int uart_id = 0;
     if (MP_OBJ_IS_STR(args[0])) {
         const char *port = mp_obj_str_get_str(args[0]);
         if (0) {
 #if defined(PYBV10)
         } else if (strcmp(port, "XA") == 0) {
-            o->uart_id = PYB_UART_XA;
+            uart_id = PYB_UART_XA;
         } else if (strcmp(port, "XB") == 0) {
-            o->uart_id = PYB_UART_XB;
+            uart_id = PYB_UART_XB;
         } else if (strcmp(port, "YA") == 0) {
-            o->uart_id = PYB_UART_YA;
+            uart_id = PYB_UART_YA;
         } else if (strcmp(port, "YB") == 0) {
-            o->uart_id = PYB_UART_YB;
+            uart_id = PYB_UART_YB;
 #endif
         } else {
-            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART port %s does not exist", port));
+            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%s) does not exist", port));
         }
     } else {
-        o->uart_id = mp_obj_get_int(args[0]);
+        uart_id = mp_obj_get_int(args[0]);
+        if (uart_id < 1 || uart_id > MP_ARRAY_SIZE(pyb_uart_obj_all)) {
+            nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_ValueError, "UART(%d) does not exist", uart_id));
+        }
+    }
+
+    pyb_uart_obj_t *self;
+    if (pyb_uart_obj_all[uart_id - 1] == NULL) {
+        // create new UART object
+        self = m_new0(pyb_uart_obj_t, 1);
+        self->base.type = &pyb_uart_type;
+        self->uart_id = uart_id;
+        pyb_uart_obj_all[uart_id - 1] = self;
+    } else {
+        // reference existing UART object
+        self = pyb_uart_obj_all[uart_id - 1];
     }
 
     if (n_args > 1 || n_kw > 0) {
         // start the peripheral
         mp_map_t kw_args;
         mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
-        pyb_uart_init_helper(o, n_args - 1, args + 1, &kw_args);
+        pyb_uart_init_helper(self, n_args - 1, args + 1, &kw_args);
     }
 
-    return o;
+    return self;
 }
 
 STATIC mp_obj_t pyb_uart_init(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
@@ -366,7 +505,35 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_init_obj, 1, pyb_uart_init);
 /// Turn off the UART bus.
 STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in) {
     pyb_uart_obj_t *self = self_in;
-    uart_deinit(self);
+    self->is_enabled = false;
+    UART_HandleTypeDef *uart = &self->uart;
+    HAL_UART_DeInit(uart);
+    if (uart->Instance == USART1) {
+        HAL_NVIC_DisableIRQ(USART1_IRQn);
+        __USART1_FORCE_RESET();
+        __USART1_RELEASE_RESET();
+        __USART1_CLK_DISABLE();
+    } else if (uart->Instance == USART2) {
+        HAL_NVIC_DisableIRQ(USART2_IRQn);
+        __USART2_FORCE_RESET();
+        __USART2_RELEASE_RESET();
+        __USART2_CLK_DISABLE();
+    } else if (uart->Instance == USART3) {
+        HAL_NVIC_DisableIRQ(USART3_IRQn);
+        __USART3_FORCE_RESET();
+        __USART3_RELEASE_RESET();
+        __USART3_CLK_DISABLE();
+    } else if (uart->Instance == UART4) {
+        HAL_NVIC_DisableIRQ(UART4_IRQn);
+        __UART4_FORCE_RESET();
+        __UART4_RELEASE_RESET();
+        __UART4_CLK_DISABLE();
+    } else if (uart->Instance == USART6) {
+        HAL_NVIC_DisableIRQ(USART6_IRQn);
+        __USART6_FORCE_RESET();
+        __USART6_RELEASE_RESET();
+        __USART6_CLK_DISABLE();
+    }
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_deinit_obj, pyb_uart_deinit);
@@ -383,103 +550,175 @@ STATIC mp_obj_t pyb_uart_any(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_any_obj, pyb_uart_any);
 
-/// \method send(send, *, timeout=5000)
-/// Send data on the bus:
-///
-///   - `send` is the data to send (an integer to send, or a buffer object).
-///   - `timeout` is the timeout in milliseconds to wait for the send.
-///
+/// \method writechar(char)
+/// Write a single character on the bus.  `char` is an integer to write.
 /// Return value: `None`.
-STATIC const mp_arg_t pyb_uart_send_args[] = {
-    { MP_QSTR_send,    MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
-    { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 5000} },
-};
-#define PYB_UART_SEND_NUM_ARGS MP_ARRAY_SIZE(pyb_uart_send_args)
-
-STATIC mp_obj_t pyb_uart_send(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
-    // TODO assumes transmission size is 8-bits wide
-
-    pyb_uart_obj_t *self = args[0];
-
-    // parse args
-    mp_arg_val_t vals[PYB_UART_SEND_NUM_ARGS];
-    mp_arg_parse_all(n_args - 1, args + 1, kw_args, PYB_UART_SEND_NUM_ARGS, pyb_uart_send_args, vals);
+STATIC mp_obj_t pyb_uart_writechar(mp_obj_t self_in, mp_obj_t char_in) {
+    pyb_uart_obj_t *self = self_in;
 
-    // get the buffer to send from
-    mp_buffer_info_t bufinfo;
-    uint8_t data[1];
-    pyb_buf_get_for_send(vals[0].u_obj, &bufinfo, data);
+    // get the character to write (might be 9 bits)
+    uint16_t data = mp_obj_get_int(char_in);
 
-    // send the data
-    HAL_StatusTypeDef status = HAL_UART_Transmit(&self->uart, bufinfo.buf, bufinfo.len, vals[1].u_int);
+    // write the data
+    HAL_StatusTypeDef status = HAL_UART_Transmit(&self->uart, (uint8_t*)&data, 1, self->timeout);
 
     if (status != HAL_OK) {
-        // TODO really need a HardwareError object, or something
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_Exception, "HAL_UART_Transmit failed with code %d", status));
+        nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, (mp_obj_t)(mp_uint_t)hal_status_to_errno_table[status]));
     }
 
     return mp_const_none;
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_send_obj, 1, pyb_uart_send);
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(pyb_uart_writechar_obj, pyb_uart_writechar);
 
-/// \method recv(recv, *, timeout=5000)
+/// \method readchar()
+/// Receive a single character on the bus.
+/// Return value: The character read, as an integer.  Returns -1 on timeout.
+STATIC mp_obj_t pyb_uart_readchar(mp_obj_t self_in) {
+    pyb_uart_obj_t *self = self_in;
+    if (uart_rx_wait(self, self->timeout)) {
+        return MP_OBJ_NEW_SMALL_INT(uart_rx_char(self));
+    } else {
+        // return -1 on timeout
+        return MP_OBJ_NEW_SMALL_INT(-1);
+    }
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_readchar_obj, pyb_uart_readchar);
+
+/// \method readinto(buf, len=-1)
 ///
-/// Receive data on the bus:
+/// Read data on the bus:
 ///
-///   - `recv` can be an integer, which is the number of bytes to receive,
-///     or a mutable buffer, which will be filled with received bytes.
-///   - `timeout` is the timeout in milliseconds to wait for the receive.
+///   - `buf` is a mutable buffer which will be filled with read characters.
+///   - `len` is the maximum number of characters to read; if negative, uses len(buf).
 ///
-/// Return value: if `recv` is an integer then a new buffer of the bytes received,
-/// otherwise the same buffer that was passed in to `recv`.
-STATIC const mp_arg_t pyb_uart_recv_args[] = {
-    { MP_QSTR_recv,    MP_ARG_REQUIRED | MP_ARG_OBJ, {.u_obj = MP_OBJ_NULL} },
-    { MP_QSTR_timeout, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 5000} },
-};
-#define PYB_UART_RECV_NUM_ARGS MP_ARRAY_SIZE(pyb_uart_recv_args)
-
-STATIC mp_obj_t pyb_uart_recv(mp_uint_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
-    // TODO assumes transmission size is 8-bits wide
+/// Return value: number of characters stored in buf.
+STATIC mp_obj_t pyb_uart_readinto(mp_uint_t n_args, const mp_obj_t *pos_args) {
+    pyb_uart_obj_t *self = pos_args[0];
 
-    pyb_uart_obj_t *self = args[0];
-
-    // parse args
-    mp_arg_val_t vals[PYB_UART_RECV_NUM_ARGS];
-    mp_arg_parse_all(n_args - 1, args + 1, kw_args, PYB_UART_RECV_NUM_ARGS, pyb_uart_recv_args, vals);
-
-    // get the buffer to receive into
+    // get the buffer to read into
     mp_buffer_info_t bufinfo;
-    mp_obj_t o_ret = pyb_buf_get_for_recv(vals[0].u_obj, &bufinfo);
-
-    // receive the data
-    HAL_StatusTypeDef status = HAL_UART_Receive(&self->uart, bufinfo.buf, bufinfo.len, vals[1].u_int);
+    mp_get_buffer_raise(pos_args[1], &bufinfo, MP_BUFFER_WRITE);
+    bufinfo.len >>= self->char_width;
+
+    // adjust the length, if given
+    if (n_args == 3) {
+        mp_int_t len = mp_obj_get_int(pos_args[2]);
+        if (len >= 0 && len < bufinfo.len) {
+            bufinfo.len = len;
+        }
+    }
 
-    if (status != HAL_OK) {
-        // TODO really need a HardwareError object, or something
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_Exception, "HAL_UART_Receive failed with code %d", status));
+    // make sure we want at least 1 char, and wait for it to become available
+    if (bufinfo.len == 0 || !uart_rx_wait(self, self->timeout)) {
+        return MP_OBJ_NEW_SMALL_INT(0);
     }
 
-    // return the received data
-    if (o_ret == MP_OBJ_NULL) {
-        return vals[0].u_obj;
-    } else {
-        return mp_obj_str_builder_end(o_ret);
+    // read the chars
+    byte *buf = bufinfo.buf;
+    for (;;) {
+        int data = uart_rx_char(self);
+        if (self->char_width == CHAR_WIDTH_9BIT) {
+            *(uint16_t*)buf = data;
+            buf += 2;
+        } else {
+            *buf++ = data;
+        }
+        if (--bufinfo.len == 0 || !uart_rx_wait(self, self->timeout_char)) {
+            // return the number of chars read
+            return mp_obj_new_int((buf - (byte*)bufinfo.buf) >> self->char_width);
+        }
     }
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_recv_obj, 1, pyb_uart_recv);
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR(pyb_uart_readinto_obj, 2, pyb_uart_readinto);
 
 STATIC const mp_map_elem_t pyb_uart_locals_dict_table[] = {
     // instance methods
+
     { MP_OBJ_NEW_QSTR(MP_QSTR_init), (mp_obj_t)&pyb_uart_init_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_deinit), (mp_obj_t)&pyb_uart_deinit_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_any), (mp_obj_t)&pyb_uart_any_obj },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_send), (mp_obj_t)&pyb_uart_send_obj },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_recv), (mp_obj_t)&pyb_uart_recv_obj },
+
+    /// \method read([nbytes])
+    { MP_OBJ_NEW_QSTR(MP_QSTR_read), (mp_obj_t)&mp_stream_read_obj },
+    /// \method readall()
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readall), (mp_obj_t)&mp_stream_readall_obj },
+    /// \method readline()
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readline), (mp_obj_t)&mp_stream_unbuffered_readline_obj},
+    /// \method write(buf)
+    { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&mp_stream_write_obj },
+
+    { MP_OBJ_NEW_QSTR(MP_QSTR_writechar), (mp_obj_t)&pyb_uart_writechar_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readchar), (mp_obj_t)&pyb_uart_readchar_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readinto), (mp_obj_t)&pyb_uart_readinto_obj },
 };
 
 STATIC MP_DEFINE_CONST_DICT(pyb_uart_locals_dict, pyb_uart_locals_dict_table);
 
-mp_uint_t uart_ioctl(mp_obj_t self_in, mp_uint_t request, int *errcode, ...) {
+STATIC mp_uint_t pyb_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t size, int *errcode) {
+    pyb_uart_obj_t *self = self_in;
+    byte *buf = buf_in;
+
+    // check that size is a multiple of character width
+    if (size & self->char_width) {
+        *errcode = EIO;
+        return MP_STREAM_ERROR;
+    }
+
+    // convert byte size to char size
+    size >>= self->char_width;
+
+    // make sure we want at least 1 char
+    if (size == 0) {
+        return 0;
+    }
+
+    // wait for first char to become available
+    if (!uart_rx_wait(self, self->timeout)) {
+        // we can either return 0 to indicate EOF (then read() method returns b'')
+        // or return EAGAIN error to indicate non-blocking (then read() method returns None)
+        return 0;
+    }
+
+    // read the data
+    byte *orig_buf = buf;
+    for (;;) {
+        int data = uart_rx_char(self);
+        if (self->char_width == CHAR_WIDTH_9BIT) {
+            *(uint16_t*)buf = data;
+            buf += 2;
+        } else {
+            *buf++ = data;
+        }
+        if (--size == 0 || !uart_rx_wait(self, self->timeout_char)) {
+            // return number of bytes read
+            return buf - orig_buf;
+        }
+    }
+}
+
+STATIC mp_uint_t pyb_uart_write(mp_obj_t self_in, const void *buf_in, mp_uint_t size, int *errcode) {
+    pyb_uart_obj_t *self = self_in;
+    const byte *buf = buf_in;
+
+    // check that size is a multiple of character width
+    if (size & self->char_width) {
+        *errcode = EIO;
+        return MP_STREAM_ERROR;
+    }
+
+    // write the data
+    HAL_StatusTypeDef status = HAL_UART_Transmit(&self->uart, (uint8_t*)buf, size >> self->char_width, self->timeout);
+
+    if (status == HAL_OK) {
+        // return number of bytes written
+        return size;
+    } else {
+        *errcode = hal_status_to_errno_table[status];
+        return MP_STREAM_ERROR;
+    }
+}
+
+STATIC mp_uint_t pyb_uart_ioctl(mp_obj_t self_in, mp_uint_t request, int *errcode, ...) {
     pyb_uart_obj_t *self = self_in;
     va_list vargs;
     va_start(vargs, errcode);
@@ -502,9 +741,9 @@ mp_uint_t uart_ioctl(mp_obj_t self_in, mp_uint_t request, int *errcode, ...) {
 }
 
 STATIC const mp_stream_p_t uart_stream_p = {
-    //.read = uart_read, // TODO
-    //.write = uart_write, // TODO
-    .ioctl = uart_ioctl,
+    .read = pyb_uart_read,
+    .write = pyb_uart_write,
+    .ioctl = pyb_uart_ioctl,
     .is_text = false,
 };
 
@@ -513,6 +752,8 @@ const mp_obj_type_t pyb_uart_type = {
     .name = MP_QSTR_UART,
     .print = pyb_uart_print,
     .make_new = pyb_uart_make_new,
+    .getiter = mp_identity,
+    .iternext = mp_stream_unbuffered_iter,
     .stream_p = &uart_stream_p,
     .locals_dict = (mp_obj_t)&pyb_uart_locals_dict,
 };
diff --git a/stmhal/uart.h b/stmhal/uart.h
index 7499473c1..eb7721415 100644
--- a/stmhal/uart.h
+++ b/stmhal/uart.h
@@ -45,9 +45,11 @@ typedef enum {
 typedef struct _pyb_uart_obj_t pyb_uart_obj_t;
 extern const mp_obj_type_t pyb_uart_type;
 
-bool uart_init(pyb_uart_obj_t *uart_obj, uint32_t baudrate);
+void uart_init0(void);
+void uart_deinit(void);
+void uart_irq_handler(mp_uint_t uart_id);
+
 bool uart_rx_any(pyb_uart_obj_t *uart_obj);
 int uart_rx_char(pyb_uart_obj_t *uart_obj);
 void uart_tx_strn(pyb_uart_obj_t *uart_obj, const char *str, uint len);
 void uart_tx_strn_cooked(pyb_uart_obj_t *uart_obj, const char *str, uint len);
-
diff --git a/teensy/uart.c b/teensy/uart.c
index 48149c795..4751e3293 100644
--- a/teensy/uart.c
+++ b/teensy/uart.c
@@ -177,35 +177,6 @@ bool uart_init(pyb_uart_obj_t *uart_obj, uint32_t baudrate) {
     return uart_init2(uart_obj);
 }
 
-void uart_deinit(pyb_uart_obj_t *uart_obj) {
-#if 0
-    uart_obj->is_enabled = false;
-    UART_HandleTypeDef *uart = &uart_obj->uart;
-    HAL_UART_DeInit(uart);
-    if (uart->Instance == USART1) {
-        __USART1_FORCE_RESET();
-        __USART1_RELEASE_RESET();
-        __USART1_CLK_DISABLE();
-    } else if (uart->Instance == USART2) {
-        __USART2_FORCE_RESET();
-        __USART2_RELEASE_RESET();
-        __USART2_CLK_DISABLE();
-    } else if (uart->Instance == USART3) {
-        __USART3_FORCE_RESET();
-        __USART3_RELEASE_RESET();
-        __USART3_CLK_DISABLE();
-    } else if (uart->Instance == UART4) {
-        __UART4_FORCE_RESET();
-        __UART4_RELEASE_RESET();
-        __UART4_CLK_DISABLE();
-    } else if (uart->Instance == USART6) {
-        __USART6_FORCE_RESET();
-        __USART6_RELEASE_RESET();
-        __USART6_CLK_DISABLE();
-    }
-#endif
-}
-
 bool uart_rx_any(pyb_uart_obj_t *uart_obj) {
 #if 0
     return __HAL_UART_GET_FLAG(&uart_obj->uart, UART_FLAG_RXNE);
@@ -390,8 +361,8 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_KW(pyb_uart_init_obj, 1, pyb_uart_init);
 /// \method deinit()
 /// Turn off the UART bus.
 STATIC mp_obj_t pyb_uart_deinit(mp_obj_t self_in) {
-    pyb_uart_obj_t *self = self_in;
-    uart_deinit(self);
+    //pyb_uart_obj_t *self = self_in;
+    // TODO
     return mp_const_none;
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_uart_deinit_obj, pyb_uart_deinit);
diff --git a/tests/pyb/uart.py b/tests/pyb/uart.py
index 6e0118d15..288022fea 100644
--- a/tests/pyb/uart.py
+++ b/tests/pyb/uart.py
@@ -2,11 +2,13 @@ from pyb import UART
 
 uart = UART(1)
 uart = UART(1, 9600)
-uart = UART(1, 9600, bits=8, stop=1, parity=None)
+uart = UART(1, 9600, bits=8, parity=None, stop=1)
 print(uart)
 
 uart.init(1200)
 print(uart)
 
-uart.any()
-uart.send(1, timeout=500)
+print(uart.any())
+print(uart.write('123'))
+print(uart.write(b'abcd'))
+print(uart.writechar(1))
diff --git a/tests/pyb/uart.py.exp b/tests/pyb/uart.py.exp
index 58ded4d84..dd98e1796 100644
--- a/tests/pyb/uart.py.exp
+++ b/tests/pyb/uart.py.exp
@@ -1,2 +1,6 @@
-UART(1, baudrate=9600, bits=8, stop=1, parity=None)
-UART(1, baudrate=1200, bits=8, stop=1, parity=None)
+UART(1, baudrate=9600, bits=8, parity=None, stop=1, timeout=1000, timeout_char=0, read_buf_len=64)
+UART(1, baudrate=1200, bits=8, parity=None, stop=1, timeout=1000, timeout_char=0, read_buf_len=64)
+False
+3
+4
+None